The invention relates generally to data recovery of storage technologies, and more particularly to methods, apparatuses and systems for data recovery by adaptive and selective level conditioning and data recognition of a read channel of storage technologies.
Advances in manufacturing technologies and system architecture have led to increasingly powerful consumer electronic devices and computers. These consumer electronic devices and computers support features and applications, such as multimedia, in connection with which vast amounts of information are processed and stored. Generally, the amount of information is not only vast, but also ever-increasing.
To provide the information, storage technologies have been developed, including magnetic, optical and magneto-optical technologies. Although these technologies provide relatively large storage capabilities, the technologies generally demand ongoing improvement so as to overcome factors limiting storage capacity. Among other areas for ongoing improvement is the accurate detection of recorded data, particularly while increasing the recording density.
Detection of recorded data is conventionally accomplished using a threshold. As an example, channel bits of an optical read channel (using, for example, 1,7 run-length-limited modulation coding) are detected by comparing a read signal to a predetermined threshold: if the read signal exceeds the threshold at a particular channel-bit location, that channel-bit is considered a xe2x80x981xe2x80x99 (i.e., a mark); otherwise the channel-bit is considered a xe2x80x980xe2x80x99 (i.e., a space).
Detection against a threshold typically relies on setting an appropriate threshold. Generally, the threshold is set toward recovering recorded information within an acceptable bit error rate. To do so, the threshold optimally is set to the center of an xe2x80x9ceye-patternxe2x80x9d, the eye-pattern being a measure that indicates the amplitude and phase margins of the read signal. However, the read signal""s amplitude and phase margins tend to be affected by various parameters, including, among others, the write power, the write sensitivity of the media, the quality of the spot of the write and read drives (e.g., mark size variations), the focus offset of the write and read drives, and the recording density. For example, increased recording density tends to increase inter-symbol interference (xe2x80x9cISIxe2x80x9d) such that amplitude margins can degrade as to both marks and spaces. Moreover, because these parameters vary across systems and media, the center of the eye pattern tends to vary and, in turn, the optimal threshold setting tends to vary.
When reading channel bits of an optical channel, using any one of a plurality of coding methodologies, the correct data patterns must follow prescribed rules and protocol. For example, using 1,7 run length limited modulation coding, the highest frequency possible consists of 2T marks on space (where T=one channel bit period). Due to optical aberrations, interference, and other data reading complications, information read from optical drive occasionally does not comply with these prescribed rules, creating data reading errors.
Accordingly, it is desirable to provide for accurate detection of recorded data while accommodating increased recording density and other parameters that tend to cause the threshold to vary and margins to degrade. Further, it is desirable to insure compliance with the data coding rules for the type of recording protocol used.
Methods, circuits and systems are provided for enhancing the accuracy of detection of recorded data while accommodating increased recording density and other parameters that tend to cause the threshold to vary and margins to degrade. More specifically, methods, circuits and systems are provided that adaptively and selectively condition the levels of samples of a read signal. Additionally, the methods, circuits and systems further check the conditioned read signal for compliance with applicable data coding rules. An advantage of the method, circuit and system is that reliable margins are established for selected samples and data cross checking is implemented, thereby improving detection and accuracy of recorded data, particularly at enhanced recording density.
A circuit embodying one aspect of the present invention includes sample logic, arithmetic logic and conditioning logic. The sample logic receives samples and provides a main sample and one or more selected neighbor samples. The arithmetic logic compares the main sample to the neighbor samples toward determining satisfaction of selected conditioning criteria. If the selected conditioning criteria are satisfied, the conditioning logic selectively and adaptively affects level conditioning as to the main sample. Preferably, the conditioning is bi-level substitution, wherein either an upper substitution level or a lower substitution level is substituted for a selected main sample. Alternatively, the level conditioning can include the substitution of a logical zero or a logical one for the subject channel bit, or the creation of a parallel data value determination.
In yet a further aspect of the invention, additional circuits include compliance logic, a threshold detector (i.e., slicer) and overruling logic. The compliance logic will receive signals from conditioning logic indicating certain conditions of the main sample and selected neighbor samples. The compliance logic further checks these signals for compliance with certain protocols or coding rules. If the data is compliant with the coding rules, no further adjustments are done. However, if the data is not compliant, further checking is accomplished and, where appropriate, signals will be sent to the overruling logic to further apply level adjustment to the main sample. In one case, level adjustment includes the overruling of data detected by the slicer.
The threshold detector receives data samples from the read logic of the optical storage system. These data samples are applied to a threshold to create a preliminary determination regarding the data. Specifically, the data is preliminarily determined to be either a 1 or 0 based upon a raw threshold determination. However, as mentioned above, this threshold determination can include many errors, due to the recording density and related degraded margins. In order to correct these still existing potential errors, further circuitry (as described above) is provided for receiving this preliminary determination and overruling this initial determination where appropriate.
In summary, the circuitry is capable of applying the level conditioning criteria, and the rule compliance criteria in order to assess the accuracy of a parallel threshold determination. Subsequently, if the threshold determination did not appear to include errors, no additional processing is necessary and the initial assessment is used. The initial assessment can be accomplished using traditional bit slice technology (threshold detection), or any other appropriate technology. Alternatively, if the level of conditioning criteria indicates that an adjustment is necessary, the overruling circuitry will appropriately cancel the initial assessment and either set or reset that channel bit appropriately. Furthermore, rule compliance circuitry is included to insure that the read channel bits comply with the rules prescribed for the particular data coding methodology being used. Based on this compliance evaluation, the preliminary assessment can also be overruled as appropriate.
A method embodying the present invention comprises obtaining level conditioning parameters in association with certain reference marks of the read signal: sampling the read signal at channel bit locations to provide a plurality of samples; selecting a main sample from the plurality of samples; selecting one or more neighbor samples from the plurality of samples, the neighbor samples being disposed at predetermined distances, in channel bits, from the main sample; comparing the main sample to each of the neighbor samples to determine satisfaction of selected conditioning criteria; and applying, where the selected conditioning criteria are determined to be satisfied, level conditioning to the main sample responsive to the level conditioning parameters.
An alternative method utilizing concepts of the present invention includes a step of level conditioning as outlined above in conjunction with a parallel threshold detection and further compliance analysis. Specifically, the level conditioning above will create a preliminary logical determination as to whether the subject channel bit is a logical one or a logical zero. Utilizing this information, along with the raw read data itself, the subject channel bit is analyzed to ensure it complies with the rules of the particular data coding protocol being used. Where appropriate, the results from the level conditioning and the compliance analysis will be used to overrule the initial determination from the threshold detector.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be made to the accompanying drawings and descriptive matter in which its preferred embodiments are illustrated and described, wherein like reference numerals identify the same or similar elements.